AMERICAN ULTRA isn't the kind of movie that's going to set the world on fire. Most likely, you'll probably enjoy it when it slinks onto Netflix six months from now. If you actually do make it out to see it in theaters—it's hot outside! why not?—you might be initially excited to recommend it, then immediately stumble when trying to think of any specific merits. I'd describe it as competent, with occasional flashes of brilliance.
Jesse Eisenberg plays an amiable corner market clerk in a small West Virginia town who discovers he's an amnesiac super spy and that the CIA is trying to kill him with some other amnesiac, somewhat-less-amiable super spies. (Because at this stage in American politics, would anyone really be terribly surprised if that happened?) American Ultra's action is of the "guy hits a series of well-trained goons with ordinary household objects" school, and it's clearly shot and occasionally clever, even if nothing in the film approaches the flair of an old-school Jackie Chan sequence or the urgency of a Bourne takedown. There are really only so many household objects you can see people bludgeoned with.
If there's an area where American Ultra unequivocally succeeds, it's giving Kristen Stewart scenery to chew. She's unquestionably the best thing about the film—to the point where I liked the movie significantly less as soon as her character got demoted from protagonist to Girlfriend Who Needs to Be Rescued. For most of the proceedings, screenwriter Max Landis subverts a fair number of tropes, including letting Stewart bounce from close-combat gunplay to stoner wordplay with impressive flexibility. When the wheels fall off in the third act, it's heartbreaking—but by that point, she's covered in more slowly congealing movie blood than John McClane, and she looks absolutely at home in it.